hammer2 - more dmsg/separation work

hammer2 - more dmsg/separation work

* Use msg->tcmd in a few places.

* Remove some debugging.

* Move the iocom in the hammer2 VFS from the pmp to the hmp, allowing
  all supported PFSs to be advertised without having to mount each one.

* Preliminary work on hammer2-generated SPANs for all PFSs on a
  hammer2_volume.  Since multiple PFSs can be advertised, we can
  no longer use AUTOTXSPAN (which can only transmit one).

* More adjustments to newfs_hammer2.  When generating multiple PFSs,
  each one is given its own clid and fsid.